Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.

The Orion Nebula at different wavelengths

You've seen plenty of pictures of the Orion Nebula, but most of them (like this one) have been taken in visible light.

Image Copyright: Robert Gendler

You can see hot, blue stars, and the glow from gas which is excited by the radiation from those stars. Astronomers call this cloud of ionized hydrogen an HII region. This particular HII region in Orion is sometimes called "Messier 42", or "M42", since it was the 42nd item listed in Charles Messier's catalog of non-stellar objects in the sky. The glowing gas cloud occupies only a small fraction of the entire constellation in the visible; it's the "sword" hanging from Orion's belt.

Image Copyright: Matthew Spinelli

But there's more to the Orion Nebula than meets the eye -- literally. If you look at other wavelengths, you'll find evidence for gas and dust extending far beyond the visible extent.

Your job: make pictures of an area of the sky, 15 degrees by 15 degrees (just a bit smaller than the entire constellation), centered on the visible cloud of glowing gas. Use the SkyView Advanced Form to reveal how this region appears when viewed at different wavelengths of electromagnetic radiation. Then interpret those pictures to explain just what sort of material can be found in this part of the sky.

  1. Go to the SkyView Advanced Form Prepare to grab a set of images. Enter "M42" in the "Coordinates or Source" box. Scroll down a screen or so to reach the "Optional Parameters" section. Make the "Image Size (pixels)" 500 by 500 pixels, and the "Image Size (degrees)" 15.0. Change the "Color Table" to "B-W Linear", which will show black for absence of radiation, and white for lots of radiation. Set the "Grid" item to "Yes".
  2. Now, start getting pictures: Scroll back up to the top of the form and highlight the "Optical" survey called "SHASSA SM". This catalog shows light with a wavelength of 656.3 nm (also called "Hydrogen alpha"), which is emitted by ionized hydrogen gas. Click the "Submit Request Now" button, and wait. A new window should pop up with a picture of this part of the sky. Print out the picture so you have a hardcopy.
  3. Go back and de-select the "SHASSA SM" survey.
  4. Repeat steps 2 and 3 for the following surveys:
             Infrared:  IRAS 100 micron
             Radio:     CO               (carbon monoxide)
             Radio:     1420 MHz Bonn    (21-cm radio waves)
             X-ray:     RASS Cnt Broad   

You should have 5 pieces of paper, each showing the same region of the sky in Orion, but at a different wavelength. Now, make a hardcopy of the optical picture by Matthew Spinelli, above. It shows a slightly larger area of the sky than all the others, but you should be able to match it up; concentrate on the brightest sections of the nebulosity and on the three stars in the "belt" of Orion.

Write a brief explanation of what each of these 6 pictures tells us. Be sure to mention what is emitting the light in each case.

The entire complex of material is roughly 1500 light years away from the Earth. Look at the IRAS 100 micron image. Draw on this image a circle which you think encompasses most of the material. Use the grid on the picture to estimate the diameter of this circle in degrees. Calculate the approximate size of the Orion cloud complex, in light years.

Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.